1. Field of the Invention
The present invention relates to an exhaust purification device structured by providing a catalyst in an exhaust pipe of a vehicle or the like.
2. Description of the Related Art
In a vehicle such as a two-wheeled motor vehicle and a four-wheeled automobile, a catalyst is provided in an exhaust pipe in order to remove hydrocarbon (HC), nitrogen oxides (NOx), and the like included in exhaust gas. In Japanese Patent Application Laid-open No. 60-17220, there is disclosed a technique in which a catalyst is provided in a muffler of the exhaust pipe of the two-wheeled motor vehicle.
FIG. 8 is a sectional view showing an example of the exhaust pipe provided with the catalyst. The catalyst 100 includes an outer cylinder 102 and a catalyst main body 103 provided in the outer cylinder 102. The outer cylinder 102 is made of metal such as stainless steel. The catalyst main body 103 is formed by depositing catalyst metal on a surface of a honeycomb structure made of stainless steel or the like. The catalyst main body 103 is secured to an inner face of the outer cylinder 102 by brazing.
In fixing the catalyst 100 to the exhaust pipe 101, if an outer face of the outer cylinder 102 positioned on an outer periphery side of the catalyst main body 103 is subjected to welding, the brazed portion between the outer cylinder 102 and the catalyst main body 103 is susceptible to heat. Therefore, an end portion 102A of the outer cylinder 102 is caused to protrude from the catalyst main body 103 along a direction of an axial center O1 of the catalyst 100 and welding W5 is applied to this protruding portion, thereby preventing heat from affecting the brazed portion between the outer cylinder 102 and the catalyst main body 103.
However, if the end portion 102A of the outer cylinder 102 is caused to protrude from the catalyst main body 103, there is a useless area that does not contribute to purification of the exhaust gas in the outer cylinder 102. Therefore, this catalyst is inferior in purification performance to a catalyst in which a catalyst main body is provided throughout an inside of the outer cylinder 102 by an amount corresponding to the useless area.